Surface Morphology and Electrical Properties of ZnO:Ga Films Formed

In a previous study, it was found that the resistivity of ZnO:Ga films sputtered-deposited at 250 °C initially decreased with increasing film thickness up to 200 nm, but then began to increase. In the present study, the cause of this anomalous increase in resistivity was investigated, and was found to be related to an increase in the porosity of thicker films. For the film deposited at a nominal substrate temperature of 250 °C, this was the result of surface agglomeration due to unintentional substrate heating to about 290 °C caused by plasma irradiation during the deposition process. On the other hand, no such agglomeration was observed for undoped ZnO films, even when heated to 410 °C, indicating that the Ga doping plays a crucial role in the agglomeration process